High-frequency dielectric heating apparatus



June 21,I 1949. vR, H. ||.1v\;; 3r=|,4\.r-|k 1 2,473,881

' HIGH-FREQUENCY DIELEGTRIC HEATING ABPARATUS Filed June 25, 194e Oscillaar ggg@ Q@ 'Q WITNEssEs: IVENTOR ATTORNEY Patented June 21, 1949 HIGH-FREQUENCY DIELECTRIC' HEATING:v APPARATUS Richard H. Hagopian, Halethorpe, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application .l une 25, 1946, Serial No. 679,078

(Cl. 21B- 47) i Claims. 1

This invention relates to the dielectric heating of articles or substances of irregular shape or composition, or both, which are moved by a conveyor through a rapidly alternating electric iield. Generally such Work or charges are di'cult to heat in a uniform or desired manner when the alternating electric iield is such as is established soley by a single pair of spaced oppositely charged electrodes; although in some circumstances rotating the work as it moves through the field helps to produce a more uniform heat-treatment.

An object of my invention is to provide a ldielectric heating system of a type described for controllably heating pieces of work of a type described as they move through an alternating electric eld.

A further object of my invention is to provide a dielectric heating means of high productive capacity,

A further object of my invention is to provide a dielectric heating system which comprises a conveyor for moving the work through an electric eld which is established between spaced, outer, or principal, electrodes; the system having means for insuring a more uniform or more desirable heat-treatment of the work without necessarily requiring that the work be rotated while in the electric field.

Features, objects and innovations of my invention, in addition to the foregoing, will be discernible from the following simplied disclosure of a preferred form to which, however, I am not limited. This disclosure, disclosing the principles of my invention, comprises the following descrip tion and drawing which are to be considered in g conjunction. In the drawing:

Figures 1 and 2 are diagrammatic, elevational and plan views, respectively, of an arrangement in accordance with my invention.

Referring to the drawing, a charge or work-reu ceiving conveyor is illustrated as an endless belt l driven by any suitable driving means 2. The belt may be moved either step-by-step or continuously as is known in the art. Preferably the belt is of insulating material and has a plurality of spaced heating stations 3, each comprising a work-holding means shown as a low pedestal 4 attached to the belt. As each pedestal moves past a loading point A, it receives a piece of work 5 to be dielectrically heat-treated. Preferably,

means are provided on the pedestal for centering or setting the work in a predetermined position on it. The moving belt carries the work through an electric field to an unloading point B where the work is dumped or otherwise removed from the pedestal.

In the embodiment described, the dielectric field in which the pieces of work to be heat-treated are immersed, is initially established between, and bounded by, principal electrode-means in the form of two stationary elongated ilat parallel plate-electrodes 'l and 8. A high frequency tubeoscillator generator 9, suitably connected to the plate-electrodes, supplies the heating energy. The drawing schematically shows the generator connected across the plate-electrodes through a conductor l0 and ground connections ll. However, it is understood that, in practice, the connections may comprise a high frequency coaxial transmission line with an outer conductor grounded, or some equivalent means; and some means may be utilized if necessary, to smooth out or render ineffective any voltage wave-pattern that might otherwise tend to exist along the plateelectrodes.

Ordinarily, with nothing in the space between the plate-electrodes, the electric field across the space would be of uniform gradient. The field lines will be disturbed when a substance is introduced into the eld, but the change is usually not such as to produce the heating desired in the substance. A distinct feature of my invention resides in shaping the field lines so that they will penetrate the substance, or work, in a manner to controllably heat-treat the work. To this end, each heating station 3 on the belt is provided with inner or auxiliary electrode-means which are relatively fixed with respect to the pedestal and, hence, the moving work, but which shape the iield lines heating the work as it passes through the electric eld. These auxiliary electrodes are preferably highly conducting so as to create curved equi-potential surfaces in spots about the work being heat-treated. As shown in the drawing, these electrodes comprise a plurality of pairs of thin curved electrodes I3 and i4, each suoli electrode being disposed between a plate-elec trode and the facing side of a piece of work. These auxiliary electrodes are spaced from the work and do not completely surround it. They may be narrow pieces of metal which are solid, foraminous, or otherwise perforated. Or they may be any other iield distributing material which, preferably, does not absorb much energy from the rapidly pulsating electric eld.

The electrodes I3 and I4 are secured to the pedestals 4 and move therewith. Each auxiliary electrode is electrically free while passing between the plate-electrodes 1 and 8; by electrically free meaning that there is no electric connection to it so that it will assume a potential arising out of its particular position between the plate-electrodes 1 and. 8. vv,Being of metal,j.,each auxiliary electrode will distort the field lines and establish an equi-potential surface wherever the metal of the electrode is located. The voltage or potential difference between the auxiliary relle c trociesi-,l3 J

and I4 will be less than between the plate-elecz..

trodes 1 and 8.

The shape, size and numberyfof auxiliary*elec-.-4

trodes about each piece of work `3 wil1 determine,

the concentration of the eld lines at the different points where they penetrataitheworkfor heating it. In other Words, the eld linescan be directed into the work in a desired manner determined by the numberfshape and disposition of the selectedauxiliaryelectrodesi When. the-auxiliary-electrodes-l3 and- I4 `are out Vof the heating.velectricleld,-or as they -passA out. of the ziield, they 'maybe-grounded -byfengagfing. grounded` circuits including-resilientbrushes Itis obvious that my-invention-is subject to Wide variationin application-.andthat AI` am not limited to the embodiment disclosed I claim-.as my invention :l

1. A dielectric heatingly system comprising means .for yestablishing a dielectric-field,l said means 'comprising a pairof spacedfprimary elec-- trodes, a conveyor means l'having aplurality of spaced heating4 stations, saidconveyor --means successively progressing said `rstations between said- .primary electrodes,- eaclr of ysaid stations comprising--work-receiving means land auxiliary eld-aiecting .electrode-means secured to said,

conveyor means.-

2. A-'systemincluding that of cla-imy l bu-t characterized-r lfurther -bysaid -auxiliary electrodemeans comprising a pair of insulated metal members, each of which is between said work-receiving means and one oi said primary electrodes.

3. A dielectric heating system comprising means for establishing a dielectric field, said means comprising a pair of spaced upright primary electrodes, a conveyor means having a plurality of spaced heating stations, said cOnveyor means successively progressing said stations between said primary electrodes, each of said stations comprising means for receiving Work and a pair of insulated metal members, each of said metal members being betweensaid work-receiving means and one of said primary electrodes, said metal members being attached to said conveyor means and extending upwardly.

4. A i dielectricf .hea-ting system comprising means for producing a dielectric heating iield, said means comprising a pair of spaced upright primaryelectr-.odes adapted to have iield lines establishedtherebetween, a conveyor means having a horizontal portion provided with a worktreating stationior carrying work through the space between said upright primary electrodes, said heating station on said conveyor comprising a worker-receiving means'and 4auxiliary electrode means secured Lto said conveyor-portion andmovable-therewith for determining the concentration oi' saidlines that penetrate-the workfon said heating-stationas the'worl travels therewith through the 'space between saidprimary electrodes;

RICHARD H.VHAGOPIAN.

REFERENCESA CITED The following,referencesare ofrecord in the e oi this patent:

UNITED. STAIES." 'PATENTS Numberv Name Date.v

2,016,455 Purdy .g... ,Oct `8, 1935 2,231,457 Stephen Feb. 11, 1941 2,263,681 Hart-` Nov. ,25,Y 1941 2,315,0931` Languepin Mar. .30, 1943 2,333,412 Crandell Nov. 2, 1943 2,352,520 Dawson June 27,.-1944 2,397,615 Mittelmann s Apr.2, 1946 2,1121-,3flh` Klinel .et al. ,May 27 1947 2,436,732 '1 Rowe Feb. 24,' 1948 

